This invention relates to a fuel/air mixing arrangement of the radial inflow type for combustion apparatus such as burners in gas turbine engines. It has a particular applicability to gas-fueled gas turbines.
Both efficiency and environmental considerations mean that it has become essential to ensure that the levels of pollutant emission from combustion apparatus are kept as low as possible and various measures have been proposed with that aim in mind. For example, in the field of gas turbine engines, `lean-burn` combustion systems are well-known. In such systems, the air/fuel ratio is at or near stochiometric and, specifically when the engine is running at or near full load, harmful exhaust pollutants, specifically CO, NO.sub.x and unburnt hydrocarbons are produced in relatively small amounts. However, at lower loads, known lean-burn configurations may not be so advantageous and, inter alia, difficulty may be experienced in maintaining flame stability to the extent that flame-out may occur due to the weak fuel content and the low velocity of the mixture.
Past proposals for overcoming such problems have generally utilized complicated arrangements for adjusting the operation of the engine to improve low-load performance. Inter alia, there have been proposed fuel staging arrangements whereby fuel is injected in stages depending on the load under which the engine is operating, with additional stages being brought into operation as the engine load increases. In other arrangements, a pilot flame is maintained by injecting fuel directly and axially into the center of a swirler to give a fuel-rich central zone with improved flame stability. However, pilot flame systems usually give higher levels of pollution when operating at low load. All these various arrangements can involve fairly complicated control systems for ensuring the right amount of fuel is being injected at the right time and to the right place.